It was the week a man died on TV. I wonder if he guessed the fuss it would cause, or how weird it would be to have his name and particulars - Craig Ewert, 59, an American professor of computer science - appear on the news and in the papers. Would he have approved of the cynical 'chase for ratings', as opponents of John Zaritsky's moving documentary, Right to Die, were quick to describe it?

One imagines Ewert shrugging that one off, motor neuron disease permitting. This is a story, after all, usually torn into by others, its moral pith scrutinised by people free from the distractions of a frightening illness. Here was the chance for the man with the oxygen tube to speak - not as a curiosity but as someone like me or you. Why did he do it? Perhaps the prospect of being described as a 'suicide tourist' - the epithet of choice for people who, like Ewert, opt for an 'assisted' death in a Swiss clinic - was too dispiriting to contemplate without reply. 'Most people have a peaceful death,' he said glumly. 'That's fine for most people.'

He had a lot more to say, propped up in his chair or while he was being shaved or having his hair washed - some of it sad, some of it funny, some angry, all of it the fruit of long thought. He was in the cleft stick of knowing what he wanted to do and knowing that he didn't want to do it. 'I've got death, or I've got suffering - and then death,' he said. 'So this makes sense to me.' His wife was making the best of it. They laughed their heads off remembering how they met 37 years ago and had to elope. It was the day Martin Luther King was assassinated.

Ewert approached his final days fearfully, staring out of the taxi window into the abyss. 'Obviously, I've never done this before,' he said. 'It's kind of like your first day at school, and the big fear is "where the hell are the toilets?"' In the end he took his medicine - between sips of apple juice - like the man he had decided to be, closing his eyes on the camera and on life.

Should we have been there at the moment of truth? It seemed rude to leave.

There wasn't much cheer to chew on last week, TV having slipped out of gear before Christmas, leaving us with the dog-ends of celebrity marathons and Spooks, whose last episode found Harry and the others saving us from a Russian nuclear bomb (yes, a bit 1982, but I suppose there's no telling the KGB's capacity for bearing a grudge).

If you wanted the real end of the world, you had to watch Planet of Fire, the third in Channel 4's 'Catastrophe' popular science series, presented by Tony Robinson. 'This is the story of fireball Earth,' he said gravely, as though it was only last Tuesday teatime that a mystery phenomenon wiped out 95 per cent of all life and not, as it turned out, 250 million years ago. The clue to the mystery was in the title, of course, and the CGI people soon had a fine, roaring blaze going with planets colliding and lava exploding into the heavens and prehistoric beasts raising their great toothy heads at the watering hole as a bursting river of molten ore cracked Siberia open like a runny egg. I felt a bit downhearted when the fire went out after about 10 minutes, but we did have a lot of millennia to get through, what with the effects of unwholesome gases and acid rain - the great cooling, the great heating-up again ('It was global warming gone mad!'), the oceans bubbling pink with poison. Everything died as promised. It all took about 100,000 years, though there were moments - as the sky cleared and the dust settled into a programme about palaeontologists peering out of their beards at rock specimens and Tony incessantly recapping events for people who might have nodded off - when it seemed longer.

There was more global disquiet in Allergy Planet, more scientific furrowing of brows, more zooming graphics showing Earth from space, this time purporting to show us where California was. Whatever happened to maps? The first question, though, was why increasing numbers of us in the West have respiratory problems or can't walk through a field without our faces ballooning up. Fifty years ago no one had allergies; today you can throw a stick and hit someone who can't be in the same room as engine oil or chocolate. What is happening to us?

The quest to find out took us to the world's remotest inhabited island - Tristan da Cunha in the South Atlantic, half of whose population of 266 suffer from ... asthma! This seemed an amazing statistic but yielded a commensurately amazing story of five British soldiers garrisoned here in 1816 (guarding Napoleon on 'neighbouring' St Helena, 1,200 miles away) who sent for five wives - three of whom, against all odds, arrived with the disease. Seventy years later, two shipwrecked Italian sailors turned up who also had it. What are the chances of that? Scurvy you would have guessed. Or something venereal. Anyway, according to the Canadian professor beavering away in this community of dry-stone walls, sheepdogs, allotments and women knitting contentedly in the breeze (imagine Northumberland with a volcano in the background), all the inhabitants here were descended from the original 12 people, which suggested a strong genetic factor, coupled with quite bad luck.

But that was just one story. It didn't explain why 20 per cent of the people on Barbados had asthma, along with a host of other allergies. Here, the sudden transition from rural living to a westernised environment was the prime suspect. Concrete housing harboured more dust - and therefore dust mites - than the old tin shacks, as did carpets and upholstery. There was a poignant, lingering shot in which a row of inhalers was pictured against the nylon clash of curtains and swirly sofas and antimacassars. You could have given yourself an electric shock just crossing the room to pick one up.

Diet, cars and lack of activity also figured. Will modern life be the death of us all? The theory was that our immune system, designed to fight off parasites, is now busy fighting off harmless allergens. The old biology is out of sync with our sophisticated new selves. Dovetailing into this was another theory that our love for bathroom unguents and loofahs and detergents may be leaving our bodies vulnerable to attack. The killer fact was that when you're testing for an allergic reaction, Sellotape is enough to remove the skin barrier. Imagine then what it was like to be poor 14-year-old Billy, who had a rare disorder that saw the skin peeling off him like candle wax. Beset by the string of allergies that typically went with his condition - nuts, kiwi fruit, bees, latex, shellfish - he was living proof of the theory. Improbable as it seemed, having no skin was even worse than it looked.

There was a happy ending to this sobering programme - another young boy cured of a severe dog allergy by immuno-therapy - but the rest left you with an itch you couldn't scratch.

Thank God for BBC4. I know some of their documentaries about jazz festivals or migration can go on as long as actual jazz festivals and migrations, but they also offer more compact pleasures, such as The Medici: Makers of Modern Art. Here the affable critic Andrew Graham-Dixon, following up his interesting two-parter about Vasari in recent weeks, was back in Florence and talking Italian, often even to people who could speak English. The Medicis are remembered as the great patrons of Renaissance art, but back then they were known as bankers - or rather usurers, a class of citizen pictured in the frescoes of the local 'chapel of the inferno' being tormented by demons alongside sodomites and blasphemers. Being rich was great but who wanted to end up for eternity on the end of a hot trident? Art was the platinum get-out-of-hell card - art dedicated to the glory of the Almighty via the Church. Giovanni de Medici paid for a huge pair of fancy doors for the new Baptistry that took more than 20 years to complete. His son Cosimo built an entire monastery and rode around town on a donkey, hoping God would forget what he did for a living. Next up was Lorenzo, who founded an art school where Michelangelo was top of the class. Andrew Graham-Dixon, his tan fluctuating by the minute as he took us through the years of change wrought in art by the influence of the ancient world - the myths, the classical lines that encouraged an enthusiasm for geometry and perspective - seemed to enjoy himself. He had a laugh with a young woman over some Donatello buttocks she was restoring and even found time to sit down to a Medici feast. 'Extraordinario!' he exclaimed, when presented with a boar's leg the size of an oar. Cosimo, a big eater, died of gout, though by then he had managed to get a note from the Pope excusing him from hell.

Would that we could all go with such peace of mind.

Oceans to dive for

Remember Jacques Cousteau? No, neither do I with any clarity, though I do seem to recall that he was as swinging a part of the Sixties as Tom Jones and James Bond. It seems improbable now, but perhaps marine derring-do is due for a comeback.

Anyway here was his grandson - Jacques's not Tom's - Philippe, one of the scientists diving in the Med for the BBC's Oceans series. Part salty adventurers and part eco-worriers tutting at tuna farms, the team explored the cargo of a Roman wreck and swam with dinosaurs - well, a rare six-gill shark whose nearest ancestors are Jurassic fossils. You can only see one by being almost crippled by decompression in the violent currents (for geophysical reasons that I didn't quite take on board), so it was a treat from that point of view. Excellent. And of course it's one of those series you can just dip into ...